A large number of bird species nest in tree cavities. Some of these species excavate their own nest-holes (primary cavity-nesters such as woodpeckers (Picidae)), while other species re-use excavated holes or utilize cavities formed through processes such as fungal growth or microbial activity (secondary cavity-nesters). Many studies of cavity-nesting birds focus on species-specific life-history traits, but work on species interactions, global patterns of distribution, and ecosystem management is increasingly common. Using data from existing literature, we created the most exhaustive and complete global list of tree cavity-nesting species to date. This list serves as a base from which we aim to analyze global patterns of species interactions (in a follow-up study on ‘nest webs’), but also allows us to consider the current conservation status of cavity breeding species in the world, the extent to which secondary cavity breeders depend on primary excavators for their nest holes, and a multitude of other questions and issues. A thorough global study of tree cavity-nesting species may be key to their long-term persistence, as human alteration of natural habitat influences the availability of tree cavities, substrate for cavities, and cavity producing agents.
Results/Conclusions
Worldwide, over 1000 bird species nest in tree cavities, out of which about 50 percent are obligate tree cavity nesters. Primary excavators account for 25 percent of all cavity-nesting species, and about 30 percent of secondary cavity-nesting species rely on the holes they provide. The majority (>90%) of these species use nest holes created by woodpeckers. This study is a first step in a larger attempt to analyze patterns in the world’s tree cavity nesting birds (e.g., latitudinal patterns in the use of natural versus excavated cavities), with the aims to aid conservation and management of these species. Here, we show the importance of 1) the availability of tree cavities for over ten percent of the world’s birds, 2) primary cavity excavators in providing such cavities, and 3) the availability of dead trees and processes of natural degradation for the conservation of many bird species. Many cavity-nesting species are experiencing population declines—due to activities such as selective logging and clearing of snags—and we urge that the availability of tree cavities (and their producing agents) is seen as a key resource in future conservation planning and management.